Multi-carrier communications may include one or more channels as control channels. For example, the 3GPP Long Term Evolution (“LTE”) Release 8 (September 2009) standard provides that user equipment (“UE”) generate a physical random access channel (“PRACH”).
A PRACH may include a preamble with an expected or target length. One way of generating a PRACH is to provide an inverse fast Fourier transform (“IFFT”) engine capable of handling an input having an expected or target length of 24,576 samples. For reference, the maximum IFFT input size for other signals may only be 2,048 samples. Implementation of this method in silicon may not be trivial.
Another way of generating a PRACH is to use a hybrid frequency/time generation scheme. According to this scheme, a length of the PRACH signal at the input of the IFFT engine may be the same as for other signals. Complementary signal processing may then be applied in the time domain on the IFFT output to achieve the expected preamble length.